The present invention relates, in general, to a bearing assembly for support of a steering shaft, and more particularly to a bearing assembly including a rolling bearing having an inner ring, an outer ring, rolling bodies arranged between the inner ring and the outer ring, and a clamping ring.
Rolling bearings of this type are used for support of steering shafts in steering columns of motor vehicles. In most cases, the bearing is an angular-contact ball bearing which is used together with a further angular-contact ball bearing and forms a bearing assembly with the further angular-contact ball bearing as well as different pre-tensioning and support elements.
FIG. 1 shows a sectional view of a steering column 1 with a conventional bearing assembly. The illustration has been copied from the printed publication covering the technical seminar of the firm INA and entitled "Bearing Arrangements in the Chassis", 1988. Supported for rotational movement in a stationary steering tube 2 is a steering shaft 3 via a first angular-contact ball bearing 4 and a second angular-contact ball bearing 5. The first angular-contact ball bearing 4 and the second angular-contact ball bearing 5 are securely press-fitted with their outer rings 4a, 5a in the steering tube 2. Associated to the inner ring 4b of first angular-contact ball bearing 4 is a first clamping ring 6, and a second clamping ring 7 is associated to the inner ring 5b of second angular-contact ball bearing 5. The second clamping ring 7 is supported by a shaft shoulder 3a in axial direction and centers the inner ring 5b on the shaft. The first clamping ring 6 is biased by a helical spring 8 against the inner ring 4b. The helical spring 8 is supported thereby by a washer 9. A safety ring 10 secures the seat of the washer 9 upon the steering shaft 3 in axial direction. The pre-tensioning force of the helical spring 8 effects that the first angular-contact ball bearing 4 and the second angular-contact ball bearing 5 are pre-tensioned relative to one another. The angular-contact ball bearings 4, 5 as well as the first clamping ring 6, the second clamping ring 7, the helical spring 8, the washer 9 and the safety ring 10 are supplied during assembly of the steering column 1 as single parts and individually mounted.
German Pat. No. DE 40 13 655 C2 describes also a bearing assembly by which a steering shaft is supported in a steering tube with a first angular-contact ball bearing and a second angular-contact ball bearing. The angular-contact ball bearing are formed by an outer ring, an inner ring and rolling bodies arranged between the tracks of the outer and inner rings. Oftentimes, the rolling bodies are further guided by a cage. In each angular-contact ball bearing, the respective inner ring is guided and centered on the steering shaft by an inner clamping ring via a cone.
Angular-contact ball bearings must be biased relative to one another in order to meet their bearing function. For this purpose, for example, the inner rings are, mutually biased in this assembly by a compression spring and are supported by the respective outer ring via the rolling bodies. The compression spring may be formed by a helical spring. Oftentimes, resilient disks of also utilized for this purpose, whereby a preferred embodiment of the resilient disks are the ondular springs. The compression spring acts at one end of the bearing assembly upon the clamping ring of the first angular-contact ball bearing which clamping ring transmits in turn the axial pre-tension upon the inner ring of the first angular-contact ball bearing. When the angular-contact ball bearing is biased, the cone of the clamping ring gets jammed in an angular gap located between the inner ring and the outer surface area of the steering shaft, with the compression spring being supported by the first support element. The pre-tensioning force generated by the compression spring is transmitted via the outer rings of the angular-contact ball bearings onto the inner ring and thus onto the clamping ring of the second angular-contact ball bearing. The reactive force is absorbed by a second support element. Also the clamping ring of the second angular-contact ball bearing gets jammed with its cone in an angular gap disposed between steering shaft and inner ring, when the angular-contact ball bearings are biased relative to one another.
Depending on the size of the angular gap to be bridged between the steering shaft and the inner ring of the angular-contact ball bearing, the clamping rings are either pre-assembled before assembly of the steering column on the inner ring of the bearing, or supplied as individual parts during assembly of the steering column. A pre-assembly of the clamping ring upon the inner ring of the angular-contact ball bearing can only be realized when this angular gap is large enough so that sufficient installation space is provided for the pre-assembly of a clamping ring. In the other case, and according to the example of DE 40 13 655 C2, the clamping ring is supplied as individual parts during the assembly of the steering column and pressed with its cone like a wedge into the narrow angular gap.
A prerequisite for transmitting the pre-tensioning force of the compression spring is the fixed support in axial direction of each of the first support element and the second support element by one end of the bearing assembly. At the same time, the steering shaft is thus supported and axially secured upon the bearing assembly.
The support of the compression spring and of the clamping ring upon the steering shaft can be realized by different support elements. For example, support elements can be used which are formed in one piece with the steering shaft, such as shaft shoulders or shaft projections, or support elements are used which are secured separately on or at the steering shaft. One of these separate means which is frequently utilized is a safety ring disposed for safety purposes on the steering shaft. This safety ring is pushed during assembly of the steering column on the steering shaft and locks there in a predetermined position in a groove or claws itself in a self-locking manner in the surface of the shaft. The safety ring is thereby in contact either directly with the compression spring or the clamping ring, respectively, or its support action is supported by an additional washer. For cost reasons, the use of a groove in the steering shaft is mostly omitted, and a self-locking ring, frequently designated also as pronged ring, is used. Depending on the arrangement of the angular-contact ball bearing and its pre-tensioning elements, the pronged ring supports either the compression spring or the clamping ring.
Thus, the installation of a steering column with such a bearing assembly requires the use of several individual parts, such as at least two rolling bearings, support and safety elements, a compression spring, and in the most unfavorable case individual clamping rings as well as washers. These single parts must be individually stored before assembly and individually supplied during installation. The logistics required hereby and the costs associated therewith for the installation of such steering columns are therefore high.